Interconnection between a tractor and a trailer typically includes a wiring harness having a multi-pin electrical connection plus gladhand connections for the air brake command and air brake supply lines. Any electrical signals which are communicated from the tractor to the trailer pass via the wiring harness. Due to the limited number of wires present in an existing wiring harness and the dedicated purpose therefore, any additional electrical equipment added to a trailer requires additional wiring. Therefore it is apparent that the limitations of the existing wiring harness make it difficult to expand the number of signals which can be communicated between the tractor and trailer. For example, one limitation in the present system is techniques to communicate the diagnostic status of the trailer antilock system from the trailer to the tractor. This communication is accomplished presently by illuminating a lamp located on the trailer in view of the tractor rear view mirror when the brakes are applied. In this manner, the tractor operator is continuously informed of the diagnostic status of the trailer antilock system. It is, however, a benefit to receive and display this information on the tractor dashboard.